The purpose of this project is to determine the nature, and specificity or plasticity of trophic nerve function in the peripheral nervous system. Presently, the immunologically deficient nude mouse is being used as a recipient of xenografts (i.e., a graft from another species of animal) in order to study cross-species trophic nerve function. The results show that rat neurons can survive in xenografts in the nude mouse and that rat neurons can regenerate nerve fibers into mouse tongue tissue and induce the formation of taste buds. Other results demonstrate that rat muscle xenografts can survive and become reinnervated by motor nerve fibers of the nude mouse. It should be possible therefore to use the nude mouse as an "in vivo" recipient of human tissue grafts in order to determine whether the etiology of certain human neurological diseases (e.g., familial dysautonomia, congenital muscular dystrophy) involves an alteration of trophic function in nerve or end-organ. BIBLIOGRAPHIC REFERENCES: Zalewski, A. A.: The neural induction of taste buds in the salivary ducts of the lingual gland of Von Ebner. Exp. Neurol. 52: 565-580, 1976. Zalewski, A. A., Creswell, G. F., Goshgarian, H. G., and Oh, T. H.: The nude mouse: An in vivo model for demonstrating cross-species trophic nerve function. Exp. Neurol. 54: 397-402, 1977.